1. Field of the Invention
The present invention is generally related to a light string, and more particularly, the present invention relates to a light string employing light emitting diodes (LEDs) with a constant voltage supply and voltage adjustable characteristics.
2. Discussion of the Background
LED-based light strings are used for a variety of applications, primarily for decorative purposes such as for Christmas lighting. LEDs are increasingly employed as a basic lighting source in a variety of forms, as LEDs have several favorable physical properties, such as cool operation and ability to operate under wide temperature variations. LEDs are currently available in many colors, allowing for light strings available in different colors or multicolors. An LED light string with different color LEDs typically requires different voltages for the different color LEDs. For example, the average voltage operating a white LED varies in a range from 3.0 to 3.6 volts, while the average voltage operating a red LED varies in a range from 1.8 volt to 2.2 volts.
Generally, light strings employ LEDs connected electrically in series rather than in parallel. One particular drawback to these types of light strings is that when an LED is removed from its support socket, the entire series is rendered inoperable. In a conventional light string that employs LEDs connected electrically in parallel, a plurality of light strings with LEDs in a parallel connection are coupled in a shunt circuit fashion to form a light string block, and a resistor is engaged in series between the power supply and the light string block. However, the regulating resistor is firmly welded in the string and incapable of being replaced. Thus, when the respective light strings of the block have different voltage requirements, the resistor in series cannot perform a regulating function due to different voltage requirements of different colored light strings.
In another conventional light string with LEDs connected in parallel, each of the LEDs employs a resistor in either an input connection or an output connection serving a regulating purpose. However, in the forementioned conventional light string, each of the LEDs has to be welded with a regulating resistor, which results in difficult manufacturing issues. In addition, during a welding process, the LEDs are often destroyed. Moreover, the welding renders the resistor unreplaceable. Further, when the voltage is insufficient, luminosity of the LEDs is low, and when the voltage is grossly excessive, the LEDs will burn out.